Connectivity and nestedness of the meta-community structure of moss dwelling bdelloid rotifers along a stream

We analyzed meta-community structure of bdelloid rotifers colonizing mosses along an 80 meter section of Rio Valnava in NW Italy. Bdelloid rotifers are small animals living associated with a substratum; colonization in bdelloids can be produced by active animals moving along the riverbed, or by passive dormant propagules, moved by wind. To detect which kind of colonization might be stronger at different spatial scales, we designed a spatially nested sampling experiment at three hierarchical levels: (1) single sample, (2) 10 communities inside each pool, (3) complete section of 10 pools. Assessing species richness and species similarity of communities, and coherence and nestedness of bdelloid meta-communities, we found that different forces may drive species composition at different spatial scales: at the largest scale, colonization of propagules may over-ride direct dispersal between pools, while at the scale of the single pool, differential movements of species give a nested structure to the meta-communities. The number of species increased as the level of analysis increased, even though this study was carried out along only a small stream section.